Abstract

We discuss the thermal properties of small metal and insulating structures, interesting for bolometer applications. We report on the characterization of thin-filmthermometers based on normal metal–insulator–superconductor tunnel junctions, operating at sub-Kelvin temperature and fabricated by using either niobium or aluminum as superconducting electrodes. The effect of different bias methods on the thermometer current–voltage characteristics is measured as well as the response of small metal structures to absorbed/removed power. The characterization is performed with a helium-3 refrigerator, compatible with the instrumentation generally available in ground or space-borne experiments.